The response to hormones is studied in an epithelium as it forms in culture. Epithelia formed by A6 cells, derived from kidney of Xenopus laevis, do not respond to vasopressin when grown on a petri dish. When grown on a millipore filter bottom cup, the epithelia respond to vasopressin. After seeding on a filter, the responsiveness of each subunit of adenylate cyclase was evaluated over a period of two weeks. cAMP accumulation was measured in response to stimulation of hormone receptor (by vasopressin), G nucleotide binding regulatory subunit (by cholera toxin), and catalytic subunit of adenylate cyclase (by forskolin). Evaluation was also performed by assays of adenylate cyclase activity in membrane rich fractions prepared from homogenates of the epithelia. Each subunit develops with a different time course.